Alow Earth orbit (LEO) is anorbit around Earth with aperiod of 128 minutes or less (making at least 11.25 orbits per day) and aneccentricity less than 0.25.[1] Most of the artificial objects inouter space are in LEO, peaking in number at an altitude around 800 km (500 mi),[2] while the farthest in LEO, beforemedium Earth orbit (MEO), have an altitude of 2,000 kilometers, about one-third of theradius of Earth and near the beginning of theinner Van Allen radiation belt.
The termLEO region is used for the area of space below analtitude of 2,000 km (1,200 mi) (about one-third of Earth's radius).[3] Objects in orbits that pass through this zone, even if they have anapogee further out or aresub-orbital, are carefully tracked since they present a collision risk to the many LEO satellites.
A wide variety of sources[5][6][7] define LEO in terms ofaltitude. The altitude of an object in anelliptic orbit can vary significantly along the orbit. Even forcircular orbits, the altitude above ground can vary by as much as 30 km (19 mi) (especially forpolar orbits) due to theoblateness ofEarth's spheroid figure and localtopography. While definitions based on altitude are inherently ambiguous, most of them fall within the range specified by an orbit period of 128 minutes because, according toKepler's third law, this corresponds to asemi-major axis of 8,413 km (5,228 mi). For circular orbits, this in turn corresponds to an altitude of 2,042 km (1,269 mi) above the mean radius of Earth, which is consistent with some of the upper altitude limits in some LEO definitions.
The LEO region is defined by some sources as a region in space that LEO orbits occupy.[3][8][9] Somehighly elliptical orbits may pass through the LEO region near their lowest altitude (orperigee) but are not in a LEO orbit because their highest altitude (orapogee) exceeds 2,000 km (1,243 mi).Sub-orbital objects can also reach the LEO region but are not in a LEO orbit because theyre-enter the atmosphere. The distinction between LEO orbits and the LEO region is especially important for analysis of possible collisions between objects which may not themselves be in LEO but could collide with satellites or debris in LEO orbits.
The mean orbital velocity needed to maintain a stable low Earth orbit is about 7.8 km/s (4.8 mi/s), which translates to 28,000 km/h (17,000 mph). However, this depends on the exact altitude of the orbit. Calculated for a circular orbit of 200 km (120 mi) the orbital velocity is 7.79 km/s (4.84 mi/s), but for a higher 1,500 km (930 mi) orbit the velocity is reduced to 7.12 km/s (4.42 mi/s).[10] The launch vehicle'sdelta-v needed to achieve low Earth orbit starts around 9.4 km/s (5.8 mi/s).
The pull ofgravity in LEO is only slightly less than on the Earth's surface. This is because the distance to LEO from the Earth's surface is much less than the Earth's radius. However, an object in orbit is in a permanentfree fall around Earth, because in orbit thegravitational force and thecentrifugal force balance each other out.[a] As a result, spacecraft in orbit continue to stay in orbit, and people inside or outside such craft continuously experienceweightlessness.
Objects in LEO orbit Earth between the denser part of the atmosphere and below the innerVan Allen radiation belt. They encounter atmospheric drag fromgases in thethermosphere (approximately 80–600 km above the surface) orexosphere (approximately 600 km or 400 mi and higher), depending on orbit height. Satellites in orbits that reach altitudes below 300 km (190 mi)decay quickly due to atmospheric drag.
Equatorial low Earth orbits (ELEO) are a subset of LEO. These orbits, with loworbital inclination, allow rapid revisit times over low-latitude locations on Earth.Prograde equatorial LEOs also have lowerdelta-v launch requirements because they take advantage of the Earth's rotation. Other useful LEO orbits, includingpolar orbits andSun-synchronous orbits, have higher inclinations to the equator and provide coverage for higher latitudes on Earth. Some of the first generation ofStarlink satellites used polar orbits which provide coverage everywhere on Earth. Later Starlink constellations orbit at a lower inclination and provide more coverage for populated areas.
Higher orbits includemedium Earth orbit (MEO), sometimes called intermediate circular orbit (ICO), and further above,geostationary orbit (GEO). Orbits higher than low orbit can lead to early failure of electronic components due to intenseradiation and charge accumulation.
In 2017, "very low Earth orbits" (VLEO) began to be seen inregulatory filings. These orbits, below about 450 km (280 mi), require the use of novel technologies fororbit raising because they operate in orbits that would ordinarily decay too soon to be economically useful.[11][12]
A low Earth orbit requires the lowest amount of energy for satellite placement. It provides high bandwidth and low communicationlatency. Satellites and space stations in LEO are more accessible for crew and servicing.
Since it requires lessenergy to place a satellite into a LEO, and a satellite there needs less powerful amplifiers for successful transmission, LEO is used for many communication applications, such as theIridium phone system. Somecommunication satellites use much highergeostationary orbits and move at the same angular velocity as the Earth as to appear stationary above one location on the planet.
Unlikegeosynchronous satellites, satellites in low orbit have a smallfield of view and can only observe and communicate with a fraction of the Earth at a given time. This means that a large network (orconstellation) of satellites is required to provide continuous coverage.
Satellites at lower altitudes of orbit are in the atmosphere and suffer from rapidorbital decay, requiring either periodic re-boosting to maintain stable orbits, or the launching of replacements for those that re-enter the atmosphere. The effects of adding such quantities of vaporized metals to Earth'sstratosphere are potentially of concern but currently unknown.[13]
TheInternational Space Station is in LEO about 400 to 420 kilometres (250 to 260 mi) above the Earth's surface.[14] The station's orbit decays by about 2 km/month (1.2 mi/month) and consequently needs re-boosting a few times a year.
Earth observation satellites, also known asremote sensing satellites, includingspy satellites and otherEarth imaging satellites, use LEO as they are able to see the surface of the Earth more clearly by being closer to it. A majority of artificialsatellites are placed in LEO.[15] Satellites can also take advantage of consistent lighting of the surface below viaSun-synchronous LEO orbits at an altitude of about 800 km (500 mi) and near polar inclination.Envisat (2002–2012) is one example.
GOCE (2009-2013), anESA gravimetry mission, orbited at about 255 km (158 mi).
Super Low Altitude Test Satellite (2017-2019), nicknamedTsubame, orbited at 167.4 km (104.0 mi), the lowest altitude ever among Earth observation satellites.[16]
This sectionis missing information about debris lifespan. Please expand the section to include this information. Further details may exist on thetalk page.(August 2023)
The LEO environment is becoming congested withspace debris because of the frequency of object launches.[18] This has caused growing concern in recent years, since collisions at orbital velocities can be dangerous or deadly. Collisions can produce additional space debris, creating adomino effect known asKessler syndrome.NASA's Orbital Debris Program tracks over 25,000 objects larger than 10 cm diameter in LEO, while the estimated number between 1 and 10 cm is 500,000, and the number of particles bigger than 1 mm exceeds 100 million.[19] The particles travel at speeds up to 7.8 km/s (28,000 km/h; 17,500 mph), so even a small impact can severely damage a spacecraft.[20]
^It is important to note here that "free fall" by definition requires thatgravity is the only force acting on the object. That definition is still fulfilled when falling around Earth, as the other force, thecentrifugal force is afictitious force.
^"Current Catalog Files".Archived from the original on 26 June 2018. Retrieved13 July 2018.LEO: Mean Motion > 11.25 & Eccentricity < 0.25
^Muciaccia, Andrea (2021).Fragmentations in low Earth orbit: event detection and parent body identification (Thesis).doi:10.13140/RG.2.2.27621.52966.
^ab"IADC Space Debris Mitigation Guidelines"(PDF). INTER-AGENCY SPACE DEBRIS COORDINATION COMMITTEE: Issued by Steering Group and Working Group 4. September 2007.Archived(PDF) from the original on 17 July 2018. Retrieved17 July 2018.Region A, Low Earth Orbit (or LEO) Region – spherical region that extends from the Earth's surface up to an altitude (Z) of 2,000 km
^"Artemis II".NASA. 3 April 2025. Retrieved6 August 2025.
^"Frequently Asked Questions". FAA.Archived from the original on 2 June 2020. Retrieved14 February 2020.LEO refers to orbits that are typically less than 2,400 km (1,491 mi) in altitude.
^Campbell, Ashley (10 July 2015)."SCaN Glossary". NASA.Archived from the original on 3 August 2020. Retrieved12 July 2018.Low Earth Orbit (LEO): A geocentric orbit with an altitude much less than the Earth's radius. Satellites in this orbit are between 80 and 2000 kilometers above the Earth's surface.
^"What Is an Orbit?".NASA. David Hitt : NASA Educational Technology Services, Alice Wesson : JPL, J.D. Harrington : HQ;, Larry Cooper : HQ;, Flint Wild : MSFC;, Ann Marie Trotta : HQ;, Diedra Williams : MSFC. 1 June 2015.Archived from the original on 27 March 2018. Retrieved8 July 2018.LEO is the first 100 to 200 miles (161 to 322 km) of space.{{cite news}}: CS1 maint: others (link)
^Holli, Riebeek (4 September 2009)."NASA Earth Observatory".earthobservatory.nasa.gov.Archived from the original on 27 May 2018. Retrieved28 November 2015.
